This application is a 371 of PCT/EP99/09732 filed Jul. 25, 1999.
The present invention addresses a process for manufacturing crystalline fructose by crystallizing/solidifying a purified and concentrated fructose syrup.
The preparation of crystalline fructose from sugar syrups, particularly syrups containing both fructose and glucose is known per se but involves a number of practical problems.
U.S. Pat. No. 2,588,449 discloses a process for preparing crystals of fructose dihydrate C6H12O6.2H2O, by cooling and seeding a fructose solution. However, the product obtained thereby, fructose dihydrate, is only stable at relatively low temperatures and can be neither stored nor transported without particular precautions to prevent liquefaction thereof.
On the other hand the so-called xe2x80x9canhydrousxe2x80x9d fructose (see U.S. Pat. No. 3,513,023) is known. The methods for crystallizing this product are either relatively complex and costly, e.g. using alcoholic solutions (see U.S. Pat. No. 3,607,392), or appear to be ineffective in practice due to isomerization of fructose in the aqueous phase. Particularly, this is the case of the process according to U.S. Pat. No. 3,513,023: when the conditions claimed by this patent are recreated experimentally, it happens that fructose xe2x80x9cmutarotationxe2x80x9d (equilibrium reaction between the five isomers of fructose, i.e. beta-D-fructopyranose, beta-D-fructofuranose, alpha-D-fructofuranose, alpha-D-fructopyranose and the ketonic, noncyclic form of fructose) causes the formation of noncrystallizable isomers, which considerably affects crystallization by solidification.
The present invention has the object to provide a new fructose crystallization process while obviating the problems of prior art and to obtain a form of commercially useable crystalline fructose.
The present invention relates to a method for making crystallized fructose comprising preparing a pure fructose syrup by melting fructose dihydrate crystals, concentrating the melt by heating under reduced pressure to obtain a dry matter content above 96% by weight, seeding the concentrated syrup with fructose crystals, and solidifying the seeded syrup. In a preferred process, the time between the melting the fructose dihydrate crystals and the concentration of the syrup to a dry matter content above 96% by weight is less than 24 hours, preferably less than 8 hours. The invention also relates to crystallized fructose produced by the process of the present invention wherein the fructose is comprised primarily of the beta-D-fructopyranose fructose crystals tautomers with low amounts of other fructose tautomers which are considered impurities in the crystallization context.
This new process for manufacturing crystallized fructose, including solidification of a hot and concentrated fructose solution after seeding the solution with fructose crystals is characterized by the use of a fructose solution resulting from a pure fructose syrup, freshly prepared by melting crystals of fructose dihydrate, and concentrated by evaporation in a vacuum to obtain a dry matter content above 96% by weight, and preferably above 97% by weight.
In accordance with an additional characteristic of the invention, the fructose solution used for seeding preferably has a temperature of 50 to 100xc2x0 C., ideally of 80 to 95xc2x0 C.
Also, seeding is preferably performed with 5 to 30% by weight of finely grained crystallized fructose, particularly having a particle size of less than 500 xcexcm, preferably less than 250 xcexcm (for instance 50 xcexcm).
According to another additional characteristic of the invention, the time between melting of fructose dihydrate crystals to prepare the starting syrup and concentration of said syrup to a dry matter content above 96% by weight, preferably above 97% by weight is preferably of less than 24 hours, more particularly less than 8 hours, and ideally less than half an hour.
The invention also relates to a general process for manufacturing crystallized fructose from a syrup containing fructose and possibly other substances (for instance other sugars, proteins, etc.), including the following successive steps:
seeding, with crystals of fructose dihydrate, the aqueous solution of fructose having a total sugar content of 45 to 65% by weight and a fructose content above 60% by weight, referred to the dry matter, at a temperature of 10 to xe2x88x9210xc2x0 C.,
keeping the solution in fructose supersaturation conditions, by progressively lowering temperature until crystals of the desired size are obtained, and
separating the crystals obtained from the mother liquor to obtain crystals of fructose dihydrate having a fructose content of 95 to 100% by weight referred to the dry matter;
melting the crystals collected in a syrup having a content of about 83% by weight of sugar and about 17% of water;
concentrating the syrup obtained thereby by water evaporation under limited pressure, preferably a pressure of less than a column of mercury 60 mm high, until a dry matter content above 96% by weight, preferably of 97 to 100% by weight is reached;
seeding the syrup obtained thereby by means of 5 to 30% by weight of crystallized fructose, preferably at a temperature of 80 to 95xc2x0 C.;
keeping the mass obtained thereby at a temperature of 55 to 75xc2x0 C., until a nontacky and brittle mass is obtained, and
crushing, drying and grinding this mass into particles formed by crystals of agglomerated fructose.
It will be understood that a possible water addition upon melting of crystals of fructose dihydrate, and the consecutive removal of said added water upon concentration of the syrup until a dry matter content of 96 to 100% by weight is reached are absolutely equivalent to the method which provides melting of crystals as collected, provided that the time between syrup formation and concentration thereof is as short as possible (particularly below 24 hours).
The invention also relates, as a new product, to crystallized fructose, essentially consisting of beta-D-fructopyranose, having a poor content of other fructose tautomers, resulting from a method of solidification of a hot and concentrated fructose solution, after seeding the solution with crystals of fructose, in which the fructose solution used for seeding results from a pure fructose syrop freshly prepared by melting crystals of fructose dihydrate, concentrated by evaporation in a vacuum to a dry matter content of 96 to 100% by weight,
the fructose solution used for seeding preferably has a temperature of 80 to 95xc2x0 C. and seeding is performed by using 5 to 30% by weight of crystallized fructose having a particle size of less than 500 xcexcm, preferably of less than 250 xcexcm, and
the time elapsing from melting of fructose dihydrate crystals to prepare the starting syrup to concentration of said syrup to a dry matter content above 96% is of less than 8 hours, preferably less than half an hour.